1. Field of the Invention
The present invention relates to a disk-shaped recording medium, and more particularly to a multi-layered disk comprising a plurality of laminated data recording layers. Also the present invention relates to a system for recording signal in each of the data recording layers described above, and a system for reproducing signals recorded in each of the data recording layers.
2. Description of Background Information
High density storage of data in optical disks has been mainly realized by making higher a recording density in a recording surface of the disks. Also there have been made various types of effort for the same purpose by making shorter a track pitch or elevating a recording density in the linear velocity direction in scan for recording and reading in combination with efforts for making shorter a wavelength of light beam for recording emitted from a light source and signal processing in the reproducing system.
However, a wavelength of a light beam emitted from a light source can be made only in a ultraviolet region, and also pit size reduction is allowable only on the condition that the transcription to a disk can be executed in cutting, and it can be considered that the efforts for elevating a recording density in a two-dimensional region will reach a limit in the future.
A multi-layered disk formed by laminating data recording layers has been disclosed in Japanese Patent Laid-Open Publication No. H2-223030 (Japanese Patent Application No. H1-20999) or others to realize data recording at a higher density in a three-dimensional region, namely in the direction of thickness of a disk.
However, it has been turned out that the efforts are inadequate to further elevate a density of recorded data and to more smoothly record signals and reproduce the recorded signals.